Hexavalent and trivalent chromium based conversion coatings on zinc
electrodeposited steel have been investigated using X-ray photoelectron
spectroscopy (XPS) with the aim of elucidating their film chemistry. Furthermore, a
monochromatic Al Kα X-ray source was utilised and the spectra produced evaluated
using curve fitting software to elucidate oxidation state information. In addition, a
number of chromium compounds were investigated and used to complement the
curve fitting analysis for the conversion coatings.
High resolution Cr2p spectra from chromium compounds exhibited multiplet splitting
for Cr2O3. Additional satellite emissions can also be observed for Cr2O3 and Cr(OH)3.
Curve fitting of hexavalent chromium conversion coating (CCC) 2p3/2 spectra
contained both Cr(VI) and Cr(III) species with the content of the former slightly higher
when the X-ray beam take-off angle (TOA) was reduced to determine more surface
specific information. The Cr(III) content was determined to be mainly composed of
Cr(OH)3 with some Cr2O3. In comparison, trivalent CCCs were largely composed of
Cr2O3 as opposed to Cr(OH)3. Survey scans of both coatings revealed that the
trivalent CCCs had a higher relative zinc content
